Moisture sensing control for dryer

ABSTRACT

In a material moisture sensing control, an integrating switch, in series circuit with a pair of moisture sensing electrodes in a fabric drying apparatus, is operable to a conductive posture for a time delay period as a function of the dryness condition of the fabrics being dried. In one embodiment an integrating switch comprises an electrolytic cell operable to the conductive posture by current flow through the wet fabrics and operable for returning to the nonconductive condition upon the fabrics achieving a predetermined dryness condition. A transistor is operable for initiating a control function responsive to the high voltage developed across the electrolytic cell in the nonconductive condition.

United States Patent 1191 Co on v [4 July 9, 1974 MOISTURE SENSINGCONTROL FOR plex Components, Nov. 16, 1964, Electronics, pgs.

DRYER v I 67-71. [75] Inventor: Curran D. Cotton, Newton, Iowa P h E M Pl rzma xammer e er er 1n [73] Asslgnee: The Maymg Company Newton Assistdit ExaminerPail Devinsky Attorney, Agent, or Firm-William G. Landwier;Rich- [22] Filed: Nov. 2, 1973 afd Ward [21] Appl. No.: 412,455

[57] ABSTRACT [52] US. Cl 34/45, 34/48, 34/53, in a ri i e i g control,an i teg ating 318/483, 324/65 R switch, in series circuit with a pairof moisture sensing [51] Int. Cl F2611 19/00 electrodes n a a ric dryingapparatus, is operable to [58] Field of Search .1. 34/45, 46, 48, 53,55; a conductive posture for a time delay period as a func- 328/4, 293;318/483; 324/65 R tion of the dryness condition of the fabrics beingdried. in one embodiment an integrating switch com- [56] Reference Cit dprises an electrolytic cell operable to the conductive UNlTED STATESPATENTS posture by current flow through the wet fabrics and 3 301 0241/1967 smith 34/45 operable for returning to the nonconductive condition12/1968 Th 34/45 upon the fabrics achieving a predeterrrnned dryness3:555:308 1/1971 Peterson .1111: IZZY isomers condinon- A transistor isOperable 3 3,647,196 3/1972 Cotton 34/45 function responsive to the highvoltage developed 3,782,001 1/1972 Cotton 34/45 cro he ectrolytic cellin the nonconductive con- OTHER PUBLICATIONS Herbert Feitler, SimpleCell Competes With Comdition.

21 Claims, 2 Drawing Figures A '1 /7o v w; NM?

| J l 6/ /27 /75 A34.

ljo I f l l v {/74 F gas M4 /35 A25- i/ /3 PATENIED M 91974 SHEET 1 [1F2 mammal mm 3.822.482

sum 2 or 2 1 MOISTURE SENSING CONTROL FOR DRYER BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to a dryercontrol system and more particularly to a control circuit forautomatically initiating termination of operation of a dryer apparatuswhen fabrics being dried therein attain a predetermined drynesscondition.

2. Description of the Prior Art One type of 'dryer control frequentlyused for effecting automatic termination of the drying operation of afabric drying apparatus includes a pair of electrodes or conductors forsensing the electrical conductivity of the fabrics in the fabrictumbling chamber. The prior art patents show a number of specificcontrol circuits for measuring fabric dryness by means of a sensingcircuit including a resistance-capacitance circuit portion responsive tothe resistance of the fabrics across the electrodes and operable forterminating the drying operation at a preselected dryness condition asindicated by a predetermined charge on a capacitor. The

capacitor, in at least a portion of these dryness sensing controls, hasbeen operable for providing a time delay to insure proper drying andthus has been of relatively large capacitive value and accordingly ofrelatively high cost. In other systems, a timer mechanism hasadditionally been used to achieve all or part of the long time delay.Both of these systems have commonly included means responsive to thevoltage on the capacitor, such as a neon tube, for initiating a controlfuncnon.

There is, however, a continuing search for improved control systemshaving greater reliability and accuracy as well as being more compactand of lower cost.

SUMMARY OF THE INVENTION It is an object of the instant invention toprovide an improved fabric dryness sensing circuit operable forterminating the dryness sensing operation'at a desired fabric drynesscondition.

It is a further object of the instant invention to provide an improvedfabric dryness sensing circuit for directly integrating current flowthrough the wet fabrics bridging a pair of conductors.

it is a further object of the instant invention to provide an improvedfabric dryness sensing circuit including an integrating switch in seriesconnection to the fabric sensing electrodes.

it is still a further object of the instant invention to provide animproved dryness sensing circuit wherein the long time delay capacitormay be eliminated from the circuit.

It is yet a further object of the instant invention to provide animproved dryer control circuit including output means responsive to avoltage drop across an electrochemical device which is in seriesconnection with the moisture sensing electrodes whereby an intermediatesignal emitting device may be eliminated.

These objects are achieved in a fabric drying apparatus having a'drynesssensing circuit comprising an integrating switch in circuit with themoisture sensing elec trodes for directly integrating the current flowthrough the wet fabrics andfurther comprising accumulating circuit meansand dissipating circuit means for maintaining the integrating switchmeans in a predetermined electrical condition during the dryingoperation and for operating to a second electrical condition upon thefabrics reaching a predetermined moisture condition to terminate thedryness sensing operation and to initiate termination of operation ofthe apparatus.

Operation of the device and further objects and advantages thereof willbecome evident as the description proceeds and from an examination ofthe accompanying two pages of drawings.

DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferredembodiment of the invention with similar numerals referring to similarparts throughout the several views, wherein:

FIG. l is a view of a fabric drying apparatus partially broken away andsectioned and incorporating the control system of the instant invention;and

FIG. 2 is an electrical schematic diagram of a preferred circuitembodying the dryness sensing control of the instant invention.

DESCRIFTION OF A PREFERRED EMBODIMENT Referring to FIG. l there is shownthe overall construction for a clothes dryer it) including a cabinetassembly comprising a sidewall wrapper ll having generally verticalopposite side panels l3 and a rear panel 14. The sidewall wrapper 11 issupported on a base 15 which in turn is supported on ahorizontal surfacethrough a plurality of adjustable feet 16. The cabinet assembly furthercomprises a front panel 19 and top cover 20 supported on the sidewallwrapper ill. The top cover 20 includes anupwardly extending housing 21for accommodating selected controls for the dryer such as apush-to-start mechanism operated by button 22.

The front panel 19 defines a generally central access opening 23 andincludes a door 24 hinged on the front panel 119 and operable betweenopen and closed positions relative to the access opening 23. The door 24includes an outer panel 25 substantially flush with the front panel 19and an inner panel 26 having a portion that extends rearwardly into theaccess opening 23. A seal 29 supported by the inner panel 26 extendsendlessly around the rearwardly extending portion of the inner panel 26for engagement with a recessed portion 30 of the front panel 19 toeffectively provide an air sea] at the access opening 23.

Disposed within the cabinet assembly is a pair of spaced apart generallyvertical bulkheads 33 and 34. The rear bulkhead 34 is fixed to thesidewall wrapper ll by a pair of brackets such as the bracket 35 thatincludes a front fiangeconnected to the bulkhead 34 and a rear flangeconnected with the rear panel 14. The front bulkhead is similarlyconnected to the front flanges of wrapper llllwith a pair of brackets.

A generally cylindrical peripheral sidewall 36 is disposed between thestationary bulkheads 33 and 34. At the frontand at the rear of theperipheral sidewall 36 there are inwardly turned flanges comprisingrelatively short end walls 39 and 40 juxtaposed the front and rearbulkheads 33 and 34 and cooperable with the sidewall 36 to effectivelydefine a fabric tumbler 4i. A plurality of baffle members 43 are fixedto the peripheral sidewall 36 and extend into the tumbling chamber forassisting in the movement of fabrics therewithin during rotation of thefabric tumbler 411.

- 3 The front and rear bulkheads 33 and 34 include radially outwardlydisposed recess portions 44 and '45 extending axially toward thefront'and toward the rear, respectively, .of the dryer 10. Seals 49 and50 are fixed tothe bulkheads 33 and 34 in the recesses 44 and 45 and areengageable with the tumbler end walls 39 and 40 to provide an air sealat the ends of the tumbler 41. The bulkheads 33 and 34 also includegenerally annular portions 51 and 53 inwardly disposed from the recesses44 and 45 that effectively provide extensions of the end walls 39 and 40of the fabric tumbler 41.

The seal member 49, for example, disposed between the stationarybulkhead 33 and the rotatable tumbler into engagement with the frontwall 39 of the tumbler 41. The felt may be coated on one side with anantifric tion layer such as polytetrafluoroethylene to provide a smooth,more durable, and lower. friction running surface for engagement withthe tumbler end wall 39.

The front bulkhead 33 defines an access 57 into the tumbling chamberthat isosubstantially aligned with the access opening 23 in the frontpanel 19. The rear bulkhead34' defines an opening 58 to receive aperforate panel 59 through which airflow is directed into the tumblingchamber 60 from a duct system as will be shown.

The tumbler 41 is supported on a generally horizontal axis by a systemincluding a pair of rollers 61 supported on brackets 62 fixed to therear bulkhead 34 and by 'a pair of slide bearings (not shown) supportedbysimilar brackets fixed to the front bulkhead 33. The tumbler 41 couldbe supported entirely on rollers or entirely on slides as conditionspermit. a

The fabric tumbler 41 is rotated by a belt 63 encompassing the peripheryof the tumbler sidewall 36 and driven by a motor 64 mounted on the'base15.

The airflow system for the clothes dryer 10 includes 2 a heater assembly66 supported adjacent the base 15 and into which air is drawn from theatmosphere for heating prior to movement into the fabric tumblingchamber 60. The heater assembly 66 accommodates an electric heating coilas will be considered in greater detail as related to the controlcircuitry of FIG. 2. The

heater assembly 66 is connected to a generally up-- wardly extendingrear air duct 68 which conducts heated air from the heater assembly 66through the 'rearwardly extending lower air duct 75 to atmosphere.

The blower 74 includes an impeller (not shown) that is drivenby themotor 64 mounted adjacent to the blower 74 on the base 15. The generalairflow pattern within 4 the drying apparatus 10 is shown by the brokenand solid line arrows in FIG. 1.

In order to measure the electrical conductivity or resistance of thefabrics within the chamber 60, as a measure of the condition of drynessof the fabrics, electrodes or conductors and 81 are mounted within thechamber 60. In a preferred embodiment, the electrodes are in the form ofa pair of spaced-apart elongated conductor members mounted on aninsulating member 82 and in turn fixed to a lower portion of bulkhead33to provide a pair of electrically insulated contacting surfacesengageable by the fabrics tumbling within the tumbling chamber. It willbe realized that different forms of electrodes or conductors may be usedalthough the type disclosed herein is a preferred construction.

The electrical circuitry connected to the electrodes will beexplained ingreater detail in the discussion of FIG. 2 hereinbelow. It is noted,however, that the cabinet and other conductive portions of the apparatusare electrically connected to each other and are in turn connected toearth ground by conductor 87.

Referring now to FIG. 2 the control circuitry includes three conductorsthat are connectable with a conventional three-wire 240 volt,alternating current supply. For the explanation of the circuitry of FIG.2, it will be assumed that conductors and 101 are connected with thepower lines and that the conductor 103 is connected to theearth-grounded neutral line.

The energizing circuit for'the appliance includes a door switch 104connected to conductor 100 and also includes a manuallyactuatablemomentary push-tostart switch mechanism operated by button 22 and whichincludes a first single-pole single-throw momentary switch 105 and asecond single-pole double-throw momentary switch 106 to be describedfurther herein. The closing of the contacts in the push-to-start switch105 effects energization of a control relay including a coil 107 and apair of single-pole single-throw switches 108 and 109. The relay switch108 is in the heater circuit while the relay switch 109 serves as aholding switch during operation of the apparatus. The relay operation inthe control of the machine will be described in greater detail herein.

The electric heating coil 102 is connected between the first and secondpower conductors 100 and 101 by a circuit portion including the relayswitch 108, a high limit thermostat 112, a cycling thermostat 110, and acentrifugal switch 111 in the motor .64. The centrifugal switch 111 isnormally open but is operable to the closed position upon energizationof the motor 64.

The drive motor 64 is initially energized by a circuit extending fromthe first power conductor 100 through the door switch 104, push-to-startswitch 105, and through centrifugal switch 113 made to contact 114within the motor 64.-Until the motor 64 rotates at a predeterminedspeed, the run and start windings 115 and 116 are both energized throughcentrifugal switch 113 made to contact 114, but upon operation of thecentrifugal switch 113 to the normally open contact 117 the startwinding 116 is disconnected from the circuit. After initial energizationof the motor 64 and operation of the centrifugal switch 113 to thenormally open contact 117 and release of the push-to-start switch 105,the circuit for energizing the motor 64 and maintaining energizationthereof will be completed from the first power conductor 100 through thedoor switch 104, the relay holding switch109 and a conductor 1 19 to thenormally open contact 1 17 of the centrifugal switch 113.

A cool-down thermostat 120 is provided in the circuit to the motor 64and is operable to a closed position at a predetermined temperaturewithin the tumbling chamber 60 of, for example, 135 F. After the dryerapparatus has operated for a period of time with heat, the cool-downthermostat 120 will close and maintain the motor 64 energized until thetemperature within the tumbling chamber 60 is reduced to 135 F. Thiscooldown thermostat 120 therefore provides a fabric cooldown operationfollowing aheat On drying operation.

The lower portion of the circuit diagram of FIG. 2

comprises primarily the moisture sensing and auto matic terminationcircuit for the fabric drying apparatus. it is the general function ofthis sensing circuit to measure the moisture content of the tumblingfabrics during the drying operation and to initiate termination ofoperation at a particular fabric dryness condition. The circuit isoperable for utilizing the resistance of momentary electrical pathscompleted through random samples of tumbling fabrics within the dryingchamber. Generally speaking, these values of resistance are integratedand after a time delay period the control indicates the presence offabrics having a generally predetermined or preselected condition ofdryness. A- predetermined electrical condition within the circuitinitiates termination of operation through an output circuit portion.

An integrating switch provides the integration of the random momentaryresistance values. An electrochemical device, such as an electrolyticcell 125, is used as the integrating switch in the preferred embodimentof FIG. 2 and is operable as a timer or as an integrator. Operationally,the electrolytic cell 125 functions as a switch having a conductiveposture in which the resistance through the electrolytic cell isrelatively low and a nonconductive posture in which the resistancethrough the electrolytic cell is relatively high. The electrolytic cell125 is operable as a bidirectional electron or current flow integratoras will become clear from the following explanation.

More specifically, the electrolytic cell 125 is a reversiblemicro-coulometer device designed in accordance with F aradays law ofelectroplating. The device operates by means of the physical transfer ofatoms of metallic silver across an electrolyte. The device has a centralgoldelectrode, as shown schematically and desigcase. When current flowsin one direction, namely,

from the silver electrode 127 to the gold electrode 126, the positivesilver ions in the electrolyte are deposited on'the gold electrode 126.The effective, resistance of electrolytic cell 125 and the correspondingvoltage drop across the cell are low. When'current is applied in theopposite direction, namely, from gold electrode 126 to the silverelectrode 127, the silver is deplated from the gold electrode 126 butthe device still exhibits a low resistance as long as there is silverremaining on the working or gold electrode 126. As soon as the silverhas been depleted from this gold electrode 126, the

electrolytic device 125 changes to a nonconductive or high resistancestate, usually of the order of several megohms, with a correspondingvoltage rise to over 800 millivolts. a

In this specification, the convention that electrons flow by the samepath as current and in the opposite direction thereto will be used.Therefore, electron flow through the electrolytic cell from the goldelectrode 126 to the silver electrode 127 will effect a plating of thegoldelectrode 126.

Since the flow of current through the electrolytic cell 125 isaccompanied by a transfer of silver from one electrode to the other in adirect proportionality to the level and time of current flow, includingperiodic or random inputs of any time-current integral, the device is atrue integrator of the current input over a time period. At any instant,the quantity of silver on the working or gold electrode 126 representsatrue value of the integral of the current that has passed throughtheelectrolytic cell 125 during the integrating function.

As a simple timing device the electrolytic cell 125 may be given aninitial charge comprising a predeten mined plating current flow, orcurrent flow from the silver electrode 127 to the gold electrode 126,for a specific time to set or charge the device to a given level ofplating. The electrolytic cell 125 may then be used to provide a timedelay by connecting the electrolytic cell 125 to a circuit efiecting anopposite current flow through the device for a deplating of the silverfrom the gold electrode 126.

A combination of both timing and integration is utilized in the circuitof FIG. 2 as will be shown by the following detailed explanation of thecircuit and operation thereof.

To set the electrolytic cell 125 for a guaranteed minimum timingfunction, a preplating circuit portion is connected between the firstand second power lines 1110 and 1111 for effectinga plating current flowthrough the electrolytic cell 125 to condition the device to theconductive posture. The preplating circuit portion includes a rectifier129 connected to the first power line 1116 through door switch 104 whichpermits negative charging of a capacitor 136 through the momentary startswitch 106 made to the normally open contact 131. Upon the release ofthe momentary switch 106 foroperation to its normally closed contact133, the accumulated negative charge on capacitor 130 is dischargedthrough resistor 134 and through the electrolytic cell 125 and chassis135 to ground. It is noted that the capacitor 130 is negatively chargedwith an accumulation of electrons on the right-hand plate 136 of thecapacitor 136 so that the flow of electrons is through the electrolyticcell 125 from the gold electrode 126 to the silver electrode 127. Thisflow of electrons from the gold electrode 126 to the silver electrode127 corresponds by common practice, to the flow of current from thesilver electrode to the gold electrode so that silver ions are depositedon the gold electrode 126 as previously explained, to operate theelectrolytic cell 125 to the conductive posture.

It is also noted at this time that the silver electrode 127 of theelectrolytic cell 125 is connected to earth gound through the conductivechassis 135 of the apparatus. In the specific embodiment of FIG. 2, thechassis 135 is maintained disconnected from or electrically isolatedfrom the neutral line 163 within the control circuit as shown in H6. 2but is effectively connected to the earth-grounded neutral line 103 byan external ground path including the earth-grounded neutral line of anormal household supply. Such a circuit provision requires that theapparatus chassis be connected to the earth ground for operability ofthe circuit and apparatus. Further details and-explanation of operation'of such a control circuit are fully shown and claimed in 'copendingapplication Ser. No. 405,203 filed Oct. 10,

1973 by the instant inventor and assigned to the assignee of the instantapplication.

The control circuit also includes a plating circuit portion extendingfrom conductor 138 and comprising rectifier 137, resistor 139 and thepair of conductive electrodes 80 and 81 connected in series withrectifier 137, resistor 139, and junction 140. As wet fabrics contactand bridge the electrodes 80, 81, the resistance between the electrodeswill be relatively low and thus current flow therethrough will be at ahigh level. This current flow through the fabrics effects furtherplating of the electrolytic cell 125 butat a decreasing rate as thefabrics become dry and thus of higher resistance. The rectifier 137limits the plating to half cycle operation and the variable resistanceof the fabrics across the electrodes 80, 81 as a measure of the moisturecontent of the fabrics provides a variable plating signal to theelectrolytic cell 125.

The preplating circuit including capacitor 130 and the plating circuitincluding the electrodes 80, 81 may thus be considered as accumulatingcircuit means operable for effecting a plating of the electrolytic cell125.

A dissipating circuit is connected between the conductor 138 and theelectrolytic cell 125 to effectively provide a deplating of theelectrolytic cell 125 at a predetermined constant rate while the deviceremains in the conductive posture. The deplating path includes rectifier141, resistor 143, resistor 144,-and rectifier l45..lt is noted that therelative positioning of rectifiers 129 and 137 relative to 141 providesthat electrons flowing through the electrolytic cell 125 from theconductor 100 to the chassis 135 effect plating of the electrolytic cell125 whereas electrons flowing from ground and through the chassis 135,the electrolytic cell 125, and the deplating circuit includingrectifiers 145 and 141, effect a deplating of the electrolytic cell 125.Re,- sistance 146 functions with resistance 143 as a voltage divider foreffecting the current flow required for the shutdown device as will beshown.

Also included in the circuit of FIG. 2 is an output circuit portionincluding a transistor 149 having a base 150, a collector 151, and anemitter 152. The baseemitter junction 150, 152 is responsive to thevoltage drop across the electrolytic cell 125 as will be shown.

The output 4 circuit further includes a siliconcontrolled rectifier, orSCR 154, in circuit with the transistor 149. A capacitor'155 andresistor '156 are connected to the conductor 138 through the rectifier141 and function as an auxiliary'power supply for gating the SCR 154 toa conductive condition. The SCR 154 includes a path from the anode 157to cathode 158 connected in series to the relay coil 107 and triggeredto the conductive condition by the auxiliary power supply at gate 159for maintaining the relay coil 107 energized while the drying operationproceeds. A diode 163 is shown in parallel connection to the relay coil107 for conducting the self-induced current that is produced by thecollapsing magnetic field of the inductive relay coil 107 during thehalf cycle of normal deenergization. A

'snubber circuit including series-connected resistor 164 and capacitor165 is in parallel connection to the SCR anode-cathode path to protectthe SCR 154 against electrical transients.

The operation of the circuit of FIG. 2 for controlling operation of thedryer apparatus will now be described. With the door switch 104 in itsclosed position as by the closing of the door 24, manual operation ofthe pushto-start button 22 will close momentary switches 105 and 106 forenergizing the drive motor 64 and effectively energizing the controlcircuit to initiate operation of the apparatus. Initially, the circuitfor energizing the motor 64 extends from the first power line 100,through door switch 104, conductor 167, switch 105, and conductor 169 tothe centrifugal switch 113. The circuit continues through the run andstart windings and 116 connected in parallel and through a conductor 170to the neutral line 103.

At the same time, a circuit will be completed to the relay coil 107 andextending from the first power line 100, through door switch 104,conductor 167, the momentary switch 105, and conductor 138 to one sideof the coil 107. A circuit is also completed from the conductor 138through diode 141 and conductor 171 to one side of the capacitor 155 forpositive charging thereof. The capacitor 155 with resistor 156effectively provides a positive power supply for triggering the SCR 157to the conductive position. This effects energization of the relay coil107 by a circuit extending from conductor 138 and through theanode-cathode path of the SCR 157 and conductor 172 to the neutral line103. Energization of the relay coil 107 closes relay switches 108 and109. I

Upon the motor 64 reaching a predetermined speed, the centrifugal switch113 operates from the normally closed contact 114 to the normally opencontact 117 for deenergizing the start winding 116 and maintaining therun winding 115 energized by a circuit which ex tends from the firstpower line 100 through the closed door switch 104 and relay switch 109and conductor 119 to the normally open contact 117 of the centrifugalswitch 113. The closing of the relay switch 108 also energizes theheater 102 by a circuit that extends from the first power line 100through the relay switch 108, the high limit thermostat 112, the cyclingthermostat 110, the heater 102, and the centrifugal switch 111 to thesecond power line 101.

For charging capacitor 130, closing of the momentary switch 133 to itsnonnally open contact 131 completes a circuit between the first powerline 100 and the neutral line 103. Capacitor is negatively charged bythe circuit that extends from the conductor 167 through rectifier 129and through the momentary switch 106 closed to its normally open contact131 to the negative plate 136 of the capacitor 130. The positive plate174 of the capacitor 130 is connected to the neutral line 103 throughconductor 175.

At this stage of energization. the apparatus is operating with the motor64 energized for tumbling fabrics in chamber 60 and the heater 102energized to provide heat for drying the fabrics in theapparatus.

Upon manual release of the push-to-start button 22, the momentary switch106 operates to contact 133 and completes an electrical path from thenegatively charged capacitor 130 through resistance 134 and conductor176 to the electrolytic cell 125. The electrons from the negative orright-hand plate 136 of the capacitor 130 flow through the electrolyticcell 125 to ground. This flow of electrons corresponds to the flow ofcurrent through the electrolytic cell 125 for causing a plating actionto occur within the electrolytic cell and the cell 125 becomesconductive to provide a very low impedance path to ground. The chargeprovided by capacitor 130 provides a one-shot predetermined plating ofthe electrolytic cell 125 to condition it to the conductive posture andestablish a minimum period of conductive operation thereof.

With the motor 64 operating, the wet fabrics within the chamber v60 aretumbling therein for random engagement with the electrodes 80, 81. Thebridging of wet fabrics between the pair of electrodes 81) and 81completes the plating circuit between the conductor 138 and the neutralline 1113 for flow of electrons, as controlled by rectifier 137, throughthe electrolytic cell 125 to effect a further plating thereof. Thecircuit extends from the conductor 138 through rectifier 137, resistor139, the electrodes 80, 81 as bridged by the wet fabrics, and throughthe junction 140, the electrolytic cell 125, and the chassis groundingpath 135 to'the earth ground potential. This current flow continuesduring each negative half cycle at a rate depending upon the moisturecontent of the fabrics and will thus decrease in rate as the fabricsbecome more dry. The rate of plating is directly proportional to thecurrent flow throughthe electrolytic cell 125 from the silver electrode127 to the gold electrode 126 and will thus also decrease as the fabricsbecome dry. a The'voltage divider formed by resistances 143 and 146establishes a resistance network to effect a predetermined current flowthrough the electrolytic cell 125 for deplating the electrolytic cell125 at a generally constant rate. The deplating current flow extendsthrough the conductive chassis grounding path 135 and the'electrolyticcell 125 to the junction 140. Thedeplating circuit then extends from thejunction 146 through rectifier 145, resistor 144, resistor 143, andrectifier 141 to the conductor 138. The rate of deplating effected bythe current flow is substantially constant as determined by theimpedance of the deplating path.

The relative rates of charging or plating of the electrolytic cell 125through the electrodes 80, 81 and bridging fabrics as compared to thedeplating of the electrolytic cell 125 through the dissipating ordeplating circuit are thus dependent upon the fabrics attaining apredetermined dryness. It is noted thatwhile the fabrics are relativelywet at the initial portion of the cycle the rate of plating of theelectrolytic cell 125 by a circuit extending through the electrodes 80,81 and wet fabrics exceeds the the deplating rate through thedissipating circuit. As the dryness of the fabrics approach apreselected desired dryness, the constant rate of deplating exceeds theplating achieved through the electrodes 80, 81 and fabrics so that theremaining quantity of plated material on the gold electrode 126decreases. Eventually the electrolytic cell 125 becomes deplated,assumes a nonconductive posture, and exhibits a high voltage dropthereacross. This plating and deplating operation of the electrolyticcell 125 provides direct integration of the current flow through theelectrodes 80, 81 as dependent upon the moisture content of the fabricsand in addition provides the time delay period deemed necessary forproper drying.

It is desirable to provide to the operator a selection of drying cyclesor of degrees of dryness. To achieve this selectivity, the built-in timedelay may be made variable as by providing a variable component'forcapacitor 130. Alternatively, one or more of the resistors 139, 143, 1and 146 could be made variable. For convenience of explanation in thisspecification, how ever, the components are considered fixed.

When the electrolytic cell is plated, the voltage at the junction 177 isessentially the voltage drop across rectifier since the electrolyticcell 125 has a conductive posture. This same voltage is impressed acrossrectifier 179 and the base-emitter junction 1511, 152 of transistor 149.This voltage level, however, at the baseemitter junction 150, 152 oftransistor 149 is insufficient to cause transistor 149 to conduct acrossthe collector-emitter junction 151, 152. As the clothes become dry,however, the the electrolytic cell 125 be, comes deplated and changes toa relatively high impedance posture as previously shown. Theelectrolytic cell 125 thus becomes nonconductive in comparison to thepath through rectifier 179 and base-emitter junction 151), 152 oftransistor 149. Further, the increased voltage drop across theelectrolytic cell 125 is effectively impressed on the base-emitterjunction 1511, 152 of transistor 149 and with the resulting increasedcurrent flow through the base-emitter junction 150, 152 causing thetransistor 149 to become significantly more conductive across thecollector-emitter junction 151,152. The current path to the base-emitterjunction 151), 152 extends from conductor 138, through rectifier 141,resistor 143, resistor 144, and rectifier 179 to the transistor base150.

The conductive path through the transistor 149 shunts the SCR gatesignal which is provided to the SCR 154 through resistor 156. The SCR154 then ceases conduction to deenergize the relay coil 1117 and therebyopen relay switches 108 and 1119. Opening of switch 108 deenergizes theheater circuit while opening of switch 109 deenergizes the motor circuitunless the cool-down thermostat 1211 has been operated to the closedposition. lf the cool-down thermostat 1211 has closed, the motor 64 willremain energized until the thermostat-reset temperature is reached.During this time, the motor 64 remains energized by a circuit extendingbetween the first power line 101) through the door switch 104, theconductor 180, the cool-down thermostat 1211, conductor 119, and thecentrifugal switch 113 made to the normally open contact 117.

During the'cool-down period, a circuit will also be completed from thefirst power line 1111) through the cool-down thermostat 1211, conductor119, the centrifugal switch 113 made to the normally open contact 117,through conductor 169 and conductor 138 to one side of rectifier 141. Apower supply thus remains to the capacitor and permits current flowthrough resistor 143, resistor 144,- rectifier 179 and the baseemitterjunction 150,152 of transistor 149 to maintain the transistor 149conductive and the SCR 154 non conductive so that the relay coil 107remains deenergized during the cool-down operation.

Upon the temperature decreasing to the established temperature foropening the cool-down thennostat 120, the motor 64 will be deenergizedand the control circuit deenergized for effectively terminatingoperation of the apparatus.

earth grounding of the'apparatus for operability of the apparatus. Ifsuch a ground is .not present the initial preplating charge provided bythe capacitor 130 will find no path to ground through the electrolyticcell 125. Upon release of the push-to-start button22, the

transistor 149 will sense the high voltage condition and will terminateoperation of the apparatus even though the fabrics remain wet within'thetumbling chamber 60. The wet fabrics in the chamber 60 will also beunable to provide a plating of the electrolytic cell 125 because of theabsence of a complete circuit to ground.

Note also in FIG. 2 that rectifiers 145 and 179 are placed in aback-to-back relationship to prevent damage to the circuit components incase a two-wire connector is'utilized,-such as in a l20-voltgasappliance, where the user could inadvertently interchange the neutraland hot power lines at the appliance input connections. 1n the circuitof P16. 2, the neutralline 103 is connected to the emitter terminal 152of the transistor 149 and a ground line is connected to the electrolyticcell 125. Should a two-wire connection be used and should the plug bereversed, the line to the emitter 152 of transistor 149 would become thehot lineand there would be l20-volt difierential between the emitter oftransistor 149 and ground. This differential could cause damagingcurrent to flowboth through the transistor 149 and the electrolytic cell125 were it not blocked by the back-to-back relationship of rectifiers145 and 179.

' The circuit for.preplating the electrolytic cell 125 is provided toinsure proper operation of the, device and in particular .to provide theability to dry small loads. This preplating provides a guaranteed heattime so that regardless of the amount of plating or deplating the timedelay provides an insured drying operation.

' For the purposes of a particular reduction to practice of this circuitthe following values of components were utilized? capacitor 130 30 MFDcapacitors 155,165 0.1 MFD I resistor 134 200 K ohms resistor 139variable from 360 K ohms to 1.45

megohms resistor 143 820 K ohms resistor [46 33 K ohms resistor I44 285K ohms transistor 149 transistor 2N 4123 SCR 154 GB; C1038 electrolyticcell 125 Bisset Berman E Cell 560-0002 In the drawings and specificationthere has been set contemplated as circumstances may suggest or renderexpedient without departing from the spirit or scope of the invention asfurther defined in the following claims.

I claim:

l. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing a current path through said pairof conductors and wet material therebetween; electrical supply means forapplying power across said pair of conductors; integrating switch meansin series with said pair of conductors and operable for effectivelyintegrating the current flow through the material bridging said pair ofconductors as a measure of the moisture content thereof; accumulatingcircuit means operable for initially conditioning said integratingswitch means to a conductive posture and establishing a time delayperiod of conductive operation thereof and also operable for effectivelyextending said time delay period at a rate dependent upon the moisturecontent of said material; dissipating circuit means connected to saidintegrating switch means for decreasing the time delay period ofconductive operation thereof at a rate less than the extending rate tureafter a period of conductive operation which is a function of saidmaterial attaining a predetermined degree of dryness; and output meansresponsive to the nonconductive posture of said integrating switch meansindicative of the material attaining said predetermined degree ofdryness for initiating a control function.

2. A moisture sensing control as defined in claim 1 wherein saidintegrating switch means includes an electrochemical integrating deviceresponsive to current flow therethrough in a first direction foroperation to said conductive posture and responsive to current flowtherethrough in the opposite direction over a time delay period foroperating to said nonconductive posture from said conductive posture.

3. A moisture sensing control as defined by claim 1 wherein saidaccumulating circuit means includes a first circuit portion forinitially conditioning said integrating switch means to saidconductiveposture and establishing a minimum time delay period ofconductive'operation thereof and further includes a second circuitportion for extending the effective time period of conductive operationthereof at a rate dependent upon the moisture content of said material.

4. A moisture sensing control as defined in claim 1 wherein saidintegrating switch means includes an electrolytic cell operable to saidnonconductive posture for exhibiting a substantially increased voltageconcurrent with the material attaining a predetermined degree of drynessand wherein said output means includes a transistor responsive to saidsubstantially increased voltage for initiating said control function.

' 5. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing a current path through said pairof conductors and wet ma terial therebetween; electrical supply meansfor applying power across said pair of conductors; integrating switchmeans in series circuit with said pair of conductors and operable foreffectively integrating the current flow through thematerial bridgingsaid pair of conductors as a measure of the moisture content thereof;first means for initially conditioning said integrating switch means toa conductive posture and establishing a minimum time delayperiod ofconductive operation thereof; second means including the current paththrough said pair of conductors and wet material therebetween andoperable for effectively maintaining said integrating switch means insaid conductive posture by extending the effective time delay period ata rate dependent upon the moisture content of said material; third meansconnected to said integrating switch means for decreasing the time delayperiod of conductive operation thereof at a rate less than the extendingrate of said second means when said materials are relatively wet and ata rate greater than the extending rate of said second means when saidmaterials are relatively dry whereby said integrating switch means isoperated to said nonconductive posture after a time period of conductiveoperation which is a function of said material attaining a predetermineddegree of dryness; and output means responsive to the nonconductiveposture of said integrating switch means indicative of the materialattaining said predetermined degree of dryness for initiating a controlfunction. y

6. A moisture sensing control as defined in claim wherein said firstmeans includes a resistancecapacitance circuit and a momentary switchfor supplying a one-time pulse of current to said integrating switchmeans to effect the initial conditioning of said integrating switchmeans to said conductive posture.

7. A moisture sensing control as defined in claim 5 wherein saidintegrating switch means includes an electrolytic cell and wherein saidfirst means is operable for' effecting a predetermined quantity ofcharging thereof, said second means is operable for effecting anadditional quantity of charging dependent upon the moisture content ofthe material bridging said electrodes andwherein said third means isoperable for clearing the electrolytic cell at a generally constantrate.

8. A moisture sensing control as defined in claim 7 wherein said outputmeans includes a transistor responsive to a substantial increase involtage drop across said electrolytic cell.

9. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing a current path through said pairof conductors and wet material therebetween; electrical supply means forapplying power across said pair of conductors; integrating switch meansin series circuit with said pair of conductors and operable foreffectively integrating the current flow through the material bridgingsaid pair of conductors as a measure of the moisture content thereof;accumulating circuit means for initially conditioning said integratingswitch means to a conductive posture and also operable for effectivelyextending a time delay period of conductive operation thereof at a ratedependent upon the moisture content of said material; dissipatingcircuit means connected to said integrating switch means for decreasingthe time delay period of conductive operation thereof at-a rate lessthan the extending rate of said accumulating circuit means when saidmaterials are relatively wet and at a'rate greater than the extendingrate of said accumulating circuit means when said materials arerelatively dry whereby said integrating switch means is operated to saidnonconductive posture after a period of conductive operation which is afunction of said material attaining a predetermined degree of dryness;output circuit means including a transistor having a base-emitterjunction in parallel connection to said integrating switch means; andvoltage divider circuit means connected to said integrating switch meansand said base-emitter junction, said transistor being responsive to thesubstantially increased voltage drop across said integrating switchmeans in the nonconductive condition upon the material attaining saidpredetermined degree of dryness for becoming conductive to initiate acontrol function.

10. A moisture sensing control as defined in claim 9 wherein saidaccumulating circuit means and said dissipating circuit means are inparallel connection to each other and wherein said accumulating circuitmeans establishes a minimum time delay period and extends the time delayperiod dependent upon the moisture content of said material and whereinsaid dissipating circuit means decreases the effective time delay periodat a generally constant rate.

11. A moisture sensing control as defined in claim 9 whereinsaidintegrating switch means includes a bidirectional current integratingdevice responsive to current flow in one direction therethrough foroperation to said conductive posture and responsive to current flow inthe opposite direction therethrough for operation to said nonconductiveposture after a time period controlled by the amount of current in thefirst direction.

. apparatus and operative to control said apparatus in accordance withthe moisture content of material being dried therein, the combinationcomprising: electrode means including a pair of spaced conductorsengageable with the material being dried for completing an electricalpath through said pair of conductors and wet material therebetween;electrical supply means for applying power across said pair ofconductors; a bidirectional current integrating device in circuit withsaid tors and wet material therebetween and operable for effectingcurrent flow through said integrating device in said first direction toextend the effective time delay period of conductive operation at arate'dependent upon the moisture content of said material; third circuitmeans connected to said integrating device for effecting current flowthrough said integrating device in a second direction to decrease thetime delay period at a rate less than the extending rate of said secondcircuit means when said materials are relatively wet and at a rategreater than the extending rate of said second circuit means when saidmaterials are relatively dry and thus return said integrating device tosaid nonconductive posture after a period of conductive operation whichis a function of said material attaining a predetermined degree ofdryness; and output means responsive to the nonconductive posture ofsaid integrating device indicative of the material attaining saidpredetermined degree of dryness for initiating a control function.

14. A moisture sensing control as defined in claim 13 wherein saidbidirectional current integrating device includes an electrolytic cellresponsive to current flow in said first direction for becoming platedto assume said conductive posture and responsive to current flow in saidsecond direction for becoming deplated over a period of time controlledby the relative rates of plating and deplating to return to saidnonconductive posture.

15. A moisture sensing control as defined in claim 14 wherein saidsecond circuit means is operable for effecting a plating of saidelectrolytic cell at a rate dependent upon the moisture content of thematerial between said electrodes and wherein said third circuit means isoperable for effecting a generally constant deplating of saidelectrolytic cell.

16. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing an electrical path through saidpair of conductors and wet material therebetween; electrical supplymeans for applying power across said pair of conductors; an electrolyticdevice in circuit with said pair of conductors and operable between anonconductive deplated condition and a conductive plated condition;first circuit means for effecting an initial plating of saidelectrolytic device; second circuit means including the electrical paththrough said pair of conductors and wet material therebetween andoperable for effecting additional plating of said electrolytic device ata rate comprising a function of the conductivity condition of thematerial between said conductors; third circuit means connected to saidelectrolytic device for effecting a deplating thereof at a rate lessthan the plating rate effected by said second circuit means when saidmaterial is relatively wet and at rate exceeding the plating rate ofsaid second circuit means when said material is relatively dry wherebysaid electrolytic device effectively integrates the conductivitycondition of said material as a measure of the moisture content thereofduring a drying operation of said apparatus and is operated to thenonconductive condition upon the material attaining a predetermineddegree of dryness; and output circuit means responsive to thenonconductive deplated condition of said electrolytic device forinitiating a control function.

17. A moisture sensing control as defined in claim 16 wherein said firstcircuit means is operable for effecting an initial predeterminedquantity of plating of said electrolytic device, wherein said secondcircuit means is operable for effecting a plating of said electrolyticdevice at a rate proportional to the moisture content of the materialbetween said conductors and wherein said third circuit means is operablefor effecting a deplating of said electrolytic device at a generallyconstant rate.

18. A moisture sensing control as defined in claim 16 wherein saidoutput circuit means includes a transistor having a base-emitterjunction responsive to an increased voltage drop across the electrolyticdevice in said nonconductive condition for initiating said controlfunction.

19. A moisture sensing control as defined in claim 16 wherein said firstcircuit means includes a resistancecapacitance circuit and a manuallyoperable momentary switch for effecting a predetermined plating of saidelectrolytic device to initiate conductive operation of saidelectrolytic device for a predetermined period of time.

20. A moisture sensing control as defined in claim 16 wherein saidsecond circuit means provides a variable half cycle current for platingsaid electrolytic device at a rate dependent upon the moisture of thematerial bridging said conductors.

21. A moisture sensing control as defined in claim 20 wherein said thirdcircuit means includes a resistive network for providing a predetermineddeplating current flow through said electrolytic device to achieve adeplating thereof at a generally constant rate.

1. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing a current path through said pairof conductors and wet material therebetween; electrical supply means forapplying power across said pair of conductors; integrating switch meansin series with said pair of conductors and operable for effectivelyintegrating the current flow through the material bridging said pair ofconductors as a measure of the moisture content thereof; accumulatingcircuit means operable for initially conditioning said integratingswitch means to a conductive posture and establishing a time delayperiod of conductive operation thereof and also operable for effectivelyextendinG said time delay period at a rate dependent upon the moisturecontent of said material; dissipating circuit means connected to saidintegrating switch means for decreasing the time delay period ofconductive operation thereof at a rate less than the extending rate ofsaid accumulating circuit means when said materials are relatively wetand at a rate greater than the extending rate of said accumulatingcircuit means when said materials are relatively dry, said integratingswitch means being thereby operated to a nonconductive posture after aperiod of conductive operation which is a function of said materialattaining a predetermined degree of dryness; and output means responsiveto the nonconductive posture of said integrating switch means indicativeof the material attaining said predetermined degree of dryness forinitiating a control function.
 2. A moisture sensing control as definedin claim 1 wherein said integrating switch means includes anelectrochemical integrating device responsive to current flowtherethrough in a first direction for operation to said conductiveposture and responsive to current flow therethrough in the oppositedirection over a time delay period for operating to said nonconductiveposture from said conductive posture.
 3. A moisture sensing control asdefined by claim 1 wherein said accumulating circuit means includes afirst circuit portion for initially conditioning said integrating switchmeans to said conductive posture and establishing a minimum time delayperiod of conductive operation thereof and further includes a secondcircuit portion for extending the effective time period of conductiveoperation thereof at a rate dependent upon the moisture content of saidmaterial.
 4. A moisture sensing control as defined in claim 1 whereinsaid integrating switch means includes an electrolytic cell operable tosaid nonconductive posture for exhibiting a substantially increasedvoltage concurrent with the material attaining a predetermined degree ofdryness and wherein said output means includes a transistor responsiveto said substantially increased voltage for initiating said controlfunction.
 5. A moisture sensing control for use with a drying apparatusand operative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing a current path through said pairof conductors and wet material therebetween; electrical supply means forapplying power across said pair of conductors; integrating switch meansin series circuit with said pair of conductors and operable foreffectively integrating the current flow through the material bridgingsaid pair of conductors as a measure of the moisture content thereof;first means for initially conditioning said integrating switch means toa conductive posture and establishing a minimum time delay period ofconductive operation thereof; second means including the current paththrough said pair of conductors and wet material therebetween andoperable for effectively maintaining said integrating switch means insaid conductive posture by extending the effective time delay period ata rate dependent upon the moisture content of said material; third meansconnected to said integrating switch means for decreasing the time delayperiod of conductive operation thereof at a rate less than the extendingrate of said second means when said materials are relatively wet and ata rate greater than the extending rate of said second means when saidmaterials are relatively dry whereby said integrating switch means isoperated to said nonconductive posture after a time period of conductiveoperation which is a function of said material attaining a predetermineddegree of dryness; and output means responsive to the nonconductiveposture of said integrating switch means indicative of the materialattaining said predetermined degree of dryness for initiaTing a controlfunction.
 6. A moisture sensing control as defined in claim 5 whereinsaid first means includes a resistance-capacitance circuit and amomentary switch for supplying a one-time pulse of current to saidintegrating switch means to effect the initial conditioning of saidintegrating switch means to said conductive posture.
 7. A moisturesensing control as defined in claim 5 wherein said integrating switchmeans includes an electrolytic cell and wherein said first means isoperable for effecting a predetermined quantity of charging thereof,said second means is operable for effecting an additional quantity ofcharging dependent upon the moisture content of the material bridgingsaid electrodes and wherein said third means is operable for clearingthe electrolytic cell at a generally constant rate.
 8. A moisturesensing control as defined in claim 7 wherein said output means includesa transistor responsive to a substantial increase in voltage drop acrosssaid electrolytic cell.
 9. A moisture sensing control for use with adrying apparatus and operative to control said apparatus in accordancewith the moisture content of material being dried therein, thecombination comprising: electrode means including a pair of spacedconductors engageable with the material being dried for completing acurrent path through said pair of conductors and wet materialtherebetween; electrical supply means for applying power across saidpair of conductors; integrating switch means in series circuit with saidpair of conductors and operable for effectively integrating the currentflow through the material bridging said pair of conductors as a measureof the moisture content thereof; accumulating circuit means forinitially conditioning said integrating switch means to a conductiveposture and also operable for effectively extending a time delay periodof conductive operation thereof at a rate dependent upon the moisturecontent of said material; dissipating circuit means connected to saidintegrating switch means for decreasing the time delay period ofconductive operation thereof at a rate less than the extending rate ofsaid accumulating circuit means when said materials are relatively wetand at a rate greater than the extending rate of said accumulatingcircuit means when said materials are relatively dry whereby saidintegrating switch means is operated to said nonconductive posture aftera period of conductive operation which is a function of said materialattaining a predetermined degree of dryness; output circuit meansincluding a transistor having a base-emitter junction in parallelconnection to said integrating switch means; and voltage divider circuitmeans connected to said integrating switch means and said base-emitterjunction, said transistor being responsive to the substantiallyincreased voltage drop across said integrating switch means in thenonconductive condition upon the material attaining said predetermineddegree of dryness for becoming conductive to initiate a controlfunction.
 10. A moisture sensing control as defined in claim 9 whereinsaid accumulating circuit means and said dissipating circuit means arein parallel connection to each other and wherein said accumulatingcircuit means establishes a minimum time delay period and extends thetime delay period dependent upon the moisture content of said materialand wherein said dissipating circuit means decreases the effective timedelay period at a generally constant rate.
 11. A moisture sensingcontrol as defined in claim 9 wherein said integrating switch meansincludes a bidirectional current integrating device responsive tocurrent flow in one direction therethrough for operation to saidconductive posture and responsive to current flow in the oppositedirection therethrough for operation to said nonconductive posture aftera time period controlled by the amount of current in the firstdirection.
 12. A moisture sensing control as defined in claim 9 whereinsaid integrating switch means includEs an electrolytic cell responsiveto current flow in one direction through said accumulating circuit meansfor operation to said conductive posture and responsive to a generallyequal quantity of current flow in the opposite direction through saiddissipating circuit means for operation to said nonconductive posture.13. A moisture sensing control for use with a drying apparatus andoperative to control said apparatus in accordance with the moisturecontent of material being dried therein, the combination comprising:electrode means including a pair of spaced conductors engageable withthe material being dried for completing an electrical path through saidpair of conductors and wet material therebetween; electrical supplymeans for applying power across said pair of conductors; a bidirectionalcurrent integrating device in circuit with said pair of conductors andoperable between a conductive posture and a nonconductive posture foreffectively integrating the current flow through the material bridgingsaid pair of conductors as a measure of the moisture content thereof;first circuit means for effecting current flow through said integratingdevice in a first direction to condition said integrating device to saidconductive posture and establish a minimum time delay period ofconductive operation thereof; second circuit means including theelectrical path through said pair of conductors and wet materialtherebetween and operable for effecting current flow through saidintegrating device in said first direction to extend the effective timedelay period of conductive operation at a rate dependent upon themoisture content of said material; third circuit means connected to saidintegrating device for effecting current flow through said integratingdevice in a second direction to decrease the time delay period at a rateless than the extending rate of said second circuit means when saidmaterials are relatively wet and at a rate greater than the extendingrate of said second circuit means when said materials are relatively dryand thus return said integrating device to said nonconductive postureafter a period of conductive operation which is a function of saidmaterial attaining a predetermined degree of dryness; and output meansresponsive to the nonconductive posture of said integrating deviceindicative of the material attaining said predetermined degree ofdryness for initiating a control function.
 14. A moisture sensingcontrol as defined in claim 13 wherein said bidirectional currentintegrating device includes an electrolytic cell responsive to currentflow in said first direction for becoming plated to assume saidconductive posture and responsive to current flow in said seconddirection for becoming deplated over a period of time controlled by therelative rates of plating and deplating to return to said nonconductiveposture.
 15. A moisture sensing control as defined in claim 14 whereinsaid second circuit means is operable for effecting a plating of saidelectrolytic cell at a rate dependent upon the moisture content of thematerial between said electrodes and wherein said third circuit means isoperable for effecting a generally constant deplating of saidelectrolytic cell.
 16. A moisture sensing control for use with a dryingapparatus and operative to control said apparatus in accordance with themoisture content of material being dried therein, the combinationcomprising: electrode means including a pair of spaced conductorsengageable with the material being dried for completing an electricalpath through said pair of conductors and wet material therebetween;electrical supply means for applying power across said pair ofconductors; an electrolytic device in circuit with said pair ofconductors and operable between a nonconductive deplated condition and aconductive plated condition; first circuit means for effecting aninitial plating of said electrolytic device; second circuit meansincluding the electrical path through said pair of conductors and wetmatErial therebetween and operable for effecting additional plating ofsaid electrolytic device at a rate comprising a function of theconductivity condition of the material between said conductors; thirdcircuit means connected to said electrolytic device for effecting adeplating thereof at a rate less than the plating rate effected by saidsecond circuit means when said material is relatively wet and at rateexceeding the plating rate of said second circuit means when saidmaterial is relatively dry whereby said electrolytic device effectivelyintegrates the conductivity condition of said material as a measure ofthe moisture content thereof during a drying operation of said apparatusand is operated to the nonconductive condition upon the materialattaining a predetermined degree of dryness; and output circuit meansresponsive to the nonconductive deplated condition of said electrolyticdevice for initiating a control function.
 17. A moisture sensing controlas defined in claim 16 wherein said first circuit means is operable foreffecting an initial predetermined quantity of plating of saidelectrolytic device, wherein said second circuit means is operable foreffecting a plating of said electrolytic device at a rate proportionalto the moisture content of the material between said conductors andwherein said third circuit means is operable for effecting a deplatingof said electrolytic device at a generally constant rate.
 18. A moisturesensing control as defined in claim 16 wherein said output circuit meansincludes a transistor having a base-emitter junction responsive to anincreased voltage drop across the electrolytic device in saidnonconductive condition for initiating said control function.
 19. Amoisture sensing control as defined in claim 16 wherein said firstcircuit means includes a resistance-capacitance circuit and a manuallyoperable momentary switch for effecting a predetermined plating of saidelectrolytic device to initiate conductive operation of saidelectrolytic device for a predetermined period of time.
 20. A moisturesensing control as defined in claim 16 wherein said second circuit meansprovides a variable half cycle current for plating said electrolyticdevice at a rate dependent upon the moisture of the material bridgingsaid conductors.
 21. A moisture sensing control as defined in claim 20wherein said third circuit means includes a resistive network forproviding a predetermined deplating current flow through saidelectrolytic device to achieve a deplating thereof at a generallyconstant rate.